An emergency fill-in at first, Dorsey has made significant strides each week that tell him and his 49ers coaches he is becoming comfortable with the defensive scheme and his technique in San Francisco’s system.

For a sixth-year veteran who arrived uncertain of landing a starting job, Dorsey worked quietly until called upon to assume a larger role. He took over at nose tackle after Ian Williams’ season ended with a broken left ankle in Week 2 at Seattle.

“It was unknown to me,” Dorsey said Thursday. “I came in with a clear mind just to try to help as much as I can in any role that I was in. I was forced to step up and play a lot and I try to do my best at it.”

Since the Kansas City Chiefs selected him No. 5 overall in the 2008 draft out of LSU, Dorsey has dealt with the critics who questioned whether he would ever pan out as an NFL regular. He has been called a bust.

He just smiles and acknowledges he doesn’t mind the underdog status. Dorsey hardly generates the fanfare of the big playmakers alongside him like Ahmad Brooks, Aldon Smith or Justin Smith, and that’s just fine by him.

“I really do, I prefer it that way,” Dorsey said. “We have a lot of players on the front line that play well. We complement each other. You just can’t key in and focus on one guy. Everybody across the line plays well.”

When Dorsey took over in that 29-3 loss at Seattle on Sept. 15, he had one of four sacks against Russell Wilson, Dorsey’s first with the 49ers.

San Francisco is counting on him to put the pressure on again Sunday when the playoff-bound Seahawks (11-1) come to Candlestick Park trying to clinch the NFC West from the two-time reigning division champions. At 8-4, San Francisco is playing for its own playoff positioning.

Often doing his own thing with headphones on as he makes his way around the locker room and team facility, Dorsey enjoys all of the different personalities on this defense.

It didn’t take long for him to earn the respect of his new teammates. This marks the 28-year-old Dorsey’s first time switching teams after spending his initial five seasons with the Chiefs.

“When he does talk, it’s well thought out. It’s very insightful,” coach Jim Harbaugh said. “Kind of deep. But, he’s a good guy. Around the team, there’s no drama. He avoids drama, but he’s extremely competitive and strong. Good worker every day in practice. Sometimes you’ve got to take him out because he wants to keep playing.”

Williams went down on a cut block by J.R. Sweezy. Seahawks coach Pete Carroll defended his player and said it’s still in the playbook.

“It is a legal play,” Carroll said. “There was nothing wrong with that. Unfortunately, he got hurt, but there may come a time with all the safety issues that the competition committee frowns upon it.”

So, how does Dorsey avoid a similar fate?

“That’s the magic question,” he said. “That’s the question of the day.”

After last Sunday’s win against St. Louis, Harbaugh couldn’t wait to watch film of Dorsey’s day in his best game yet.

When Dorsey went down at the 9:20 mark of the first quarter against Arizona on Oct. 13 with a right hamstring injury, everybody feared it could be a lengthy injury. Then, there was Dorsey ready to suit up the following Sunday at Tennessee.

“Missed one and was right back in there,” Harbaugh said. “A quick healer on an injury that could have had him out longer. But, that speaks to his desire to contribute and to play. Can’t say enough good things about him.”

Defensive line coach Jim Tomsula has taken to helping ease the transition for Dorsey all season.

“I think he’s found a home here,” defensive coordinator Vic Fangio said. “I think that’s why he came here, one of the reasons he came here. And, he’s really gravitated toward the position. He’s mastering it. Credit to him and to Jim for bringing him along and coaching him along. And like I said, he’s still young enough, still early enough in our system, he’s going to continue to get better and better and we’re glad we have him.”